Screening and grading equipment is used in the manufacture of materials which require the separation of particles by size. In the manufacture of dispersions of a small uniform particle size, it is necessary to remove clusters or aggregates from the dispersion.
One type of sifter particularly suited for separating aggregates or coagulum from solid in liquid dispersions such as lattices, or paints, is a vertical shaft offset weight sifter, also known as a circular vibratory separator. The vibro-energy separator manufactured by Sweco Inc. and sold under the Trademark SWECO is representative of this type of separator. In the separator, two eccentric weights are attached about the upper and lower ends of a rotary shaft to impart a circular vibrational movement to the screen and attached tray or pan assemblies. The motion of the separator forms a "rope" of oversized material at the outer edge of the screen which moves around the edge of the pan.
In the separation of oversized particles from a dispersion, it is important that the dispersed phase not form clusters or aggregates and that such material be removed from the pan to prevent clogging of the screen which may result in pan overflow. In filtering large amounts of dispersions, such as a latex production run, it is necessary to minimize the down time of the filter. This requires a simple, dependable continuous method for removing oversized aggregates, clusters or coagulum from the screen's surface.
The present invention is useful in the separation of oversized particles from solid in liquid dispersions such as paints, lattices and paper coating compositions. The present invention may also be used with suspensions or slurries such as industrial slurries of coal, or in the food processing industry where solids may be suspended in a fluid such as the starch slurries. In the solid in liquid dispersions which may be filtered in accordance with the present invention, the continuous fluid phase may be water, or an aqueous based solution, or it may be a hydrocarbon, used, for example, in preparing pigment dispersions.
One of the more recent developments in the screening and sizing field is the Mogensen Sizer. This sizer consists of a number of screen decks each positioned at an increasing angle and having smaller openings. The apparatus has a large capacity and is suggested as being particularly suited to screening moist or sticky materials having a very small particle size. The screen does not have a circular motion nor does it suggest that a helical ramp would be suitable for removing coagulum and oversized particles from a fluid dispersion.
Vibratory conveyors are known. In this type of equipment, material is conveyed along a pathway by vibrations imparted to the conveyor belt. This type of apparatus is usually used in association with dry material and is not primarily used in association with dispersions or slurries. This type of conveyor does not suggest an improvement in a pan assembly for a circular vibratory separator.
Vibratory bowl feeders or sizers are known. This machine transports and/or separates small dry objects such as screws or nuts by a circulatory motion. The machine does not use a screen or filter pan assembling but rather a closed bowl.